2014年6月10日火曜日

Species dying out 1,000 times faster with humans on the scene

*Axolotls in a tray are fed with worms at the Biology Institute of the National Autonomous University of Mexico (UNAM) in Mexico City February 13, 2014. Scientists at UNAM's Biology Institute have warned the Axolotl or Mexican salamander, could be at risk of extinction in the wild in five to 10 years.

The world is on the brink of a sixth great extinction of species, a new study says. Species of animals and plants are currently dying out at least 1,000 times faster than they would without human interference.

Before humanity became dominant on earth, an average of one species per 10 million became extinct each year. But now between 100 and 1,000 per million cease to exist annually, says a study by a group of authors led by biologist Stuart Pimm of Duke University.

"We are on the verge of the sixth extinction," Pimm said. "Whether we avoid it or not will depend on our actions."

The biologists estimated prehistoric extinction rates based on molecular phylogeny, a technique that tracks relationships between different species through similarities and differences in their DNA. Phylogenic trees charted this way gave them an upper limit on background extinction, which they could then compare to modern extinction data.

The prime factor behind the high death rate is the shrinkage of natural habitats, the study published on Thursday by the journal Science says. Our less intelligent cohabitants find themselves with no place to live, as we take over and change environments to our benefit.

Other factors are the introduction of alien species into habitats thanks to human activity, climate change and unsustainable consumption by humans.

*This undated handout photo, taken in 2010, provided by Terry Goss Photography USA/Marine Photobank, shows an Oceanic whitetip shark. The oceanic whitetip shark was once one of the most plentiful predators on Earth and now is rarely seen. (AP Photo)

Scientists have evidence of five major extinction events in the past, in which large amounts of species disappeared due to a rapid, often catastrophic environmental change.

The worst of them happened some 252 million years ago and wiped out up to 96 percent of marine species and 70 percent of terrestrial vertebrate species. The cause is not known for certain, with a meteor impact, massive volcanic activity, depletion of oxygen in oceanic water and other possible hypotheses being discussed.